JPS6116415B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a composite high chromium roll having graphite crystallized in a high chromium outer shell material. Metallurgically, high chromium rolls are made up of fine chromium carbides in their base structure.
It is characterized by excellent wear resistance, but on the other hand, it has low thermal conductivity, and when used for hot rolling under the same rolling conditions, the temperature of the outermost surface of the body in contact with the rolled material is lower than that of other rolls with good thermal conductivity. The problem is that the increase is large. This is because the temperature difference on the surface of the roll cylinder adversely affects the roughness resistance, abrasion resistance, and crack resistance of the roll. One way to improve this drawback is to reduce the amount of chromium as much as possible, but carbide decreases in relation to the carbon content, making it impossible to maintain the excellent wear resistance inherent to high chromium rolls. Therefore, there is a limit. By the way, the conventional technical wisdom is that high chromium rolls have only hard carbides in their structure and no graphite crystallizes at all, and in fact, no rolls containing graphite have ever been found. According to the inventor's research, if it is possible to crystallize graphite in its composition, it is possible to improve the thermal conductivity of high chromium rolls, thereby effectively counteracting the deterioration of the rolling use characteristics mentioned above. I have come to think that it can be prevented. Based on this unique technical viewpoint, the present invention aims to provide a composite high chromium roll in which graphite is crystallized in the high chromium outer shell material as cast. That is, the present invention improves the chemical composition and composition of high chromium cast iron in order to achieve the above object.
Si2.0~3.4, Mn0.5~1.5, P0.1 or less, S0.08 or less,
An outer shell containing 4.5 to 10% Ni, 5 to 10 Cr, and 0.4 to 1.5% by weight, with the remainder essentially consisting of Fe and crystallized graphite in the composition, and high-grade cast iron, ductile cast iron, or graphite. It is characterized by being integrally welded with an inner shell made of cast steel. In general, chromium greatly contributes to the formation of carbides, and as the carbon content increases, the crystallization of graphite is suppressed. Therefore, normally only hard carbides exist in the matrix structure of high chromium cast iron, but the present invention, which has a composition within the above range. In the composite high chromium roll, a uniform distribution of fine graphite is observed in its structure. As for the inner shell material of this roll, the same various cast iron and cast steel materials as conventional ones can be used, and there is no special feature. Also, regarding the manufacturing method of this roll, after centrifugally casting high chromium cast iron having the above components, the inner shell (shaft core material) can be integrally welded and cast using a known composite technology. FIG. 1 schematically shows an example of the structure of a composite high chromium roll according to the present invention, and 1 shows an outer shell of high chromium cast iron, and 2 shows an inner shell (core material) made of various types of tough cast iron and cast steel. . The reason for limiting the range of components of the high chromium cast iron shell according to the present invention will be explained in detail below. C2.4 to 3.4% C combines with Cr to form chromium carbide, and also crystallizes fine graphite with the graphitization forming elements of Si and Ni, which will be described later. However,
This is because if C2.4% or less, chromium carbide decreases and graphite crystallization also stops, making it impossible to obtain the desired high-chromium cast iron. On the other hand, C3.4%
The above is due to the relationship with the Cr content, but in the case of the present invention, since Cr is suppressed to 10% or less, supersaturated carbon graphitizes due to the high Si and Ni contents.
This is because the amount of graphite crystallized becomes excessive and the wear resistance deteriorates. Si2.0 to 3.4 Si is necessary to crystallize graphite in high-chromium materials, and if it is less than 2.0%, this effect will not occur, and if it is more than 3.4%, graphite crystallization will be excessive and the wear resistance will deteriorate. . Regarding Si, it is more effective to crystallize graphite if the amount of Si before casting is lower than the above composition range, inoculated at the time of casting, and the composition of the final product is adjusted within the above range. be. Mn0.5-1.5% Mn is actively added together with Si to deoxidize the molten metal. This effect is insufficient when Mn is less than 0.5%,
This is because if the content exceeds 1.5%, the mechanical properties, especially the toughness, will deteriorate significantly. P0.1% or less The smaller the P content in the roll material, the more desirable it is.
The content should be 0.1% or less in order to make the material brittle. S: 0.08% or less Like P, the lower the S content, the more desirable it is, and since it also makes the material brittle, it should be kept at 0.08% or less. Ni4.5-10% Ni is actively included for the purpose of improving the matrix structure and crystallizing graphite. However, if Ni is less than 4.5%, no crystallization of graphite is observed, while if it is more than 10%, there will be an excessive amount of graphite as in the case of Si, and at the same time, retained austenite will increase and the austenite will not be stable even during subsequent heat treatment. This is because it poses a problem in terms of roughness resistance during use. Cr5~10% Cr combines with C to form Cr carbide, but 5%
% or less, there are few carbides and the wear resistance is poor.
On the other hand, if the content exceeds 10%, crystallization of graphite cannot be obtained even in the above-mentioned ranges of Ni and Si components. Mo0.4-1.5% Mo increases the quenching and tempering resistance and enters into the carbide, and is effective in increasing the hardness of the carbide and simultaneously improving the tempering and softening resistance. However, if its content is below 0.4%, such less effective, while
This is because if it exceeds 1.5%, the tendency to white iron becomes strong and graphite crystallization cannot be obtained. In addition to the above-mentioned components, the outer shell of the present invention is substantially made of Fe; however, in place of Fe, the following Nb and V can be contained as necessary in order to improve the material properties. . Nb, V 1.0% or less Nb and V are both effective in refining the casting structure, and may be contained alone or in combination at 1.0% or less as necessary. That is, if they are contained in a total amount of 1.0% or more, they combine with carbon to form VC, NbC, and Nb ₂ C, which impede crystallization of graphite and increase costs. Next, embodiments of the present invention will be described together with conventional examples. A composite high chromium roll having a body diameter of φ680, a body length of 1800 liters, and a total length of 3800 liters was manufactured as described below and subjected to various investigations. A high chromium cast iron molten metal having the chemical composition shown in Table 1 was used as the outer shell, and this was cast into a mold rotating on a centrifugal casting machine at a casting temperature of 1410°C to a wall thickness of 80 mm (casting weight 2T400Kg). After the outer shell has completely solidified (22~
After 23 minutes), the centrifugal casting mold with the outer shell inside was set vertically, and the inner shell molten metal shown in Table 1 was poured from the top as the shaft core material at 1380℃, and the inside of the mold was completely filled. , the upper end was covered with a riser heat insulator.

【table】

[Table] After completely cooling, the roll was taken out from the mold and subjected to strain relief heat treatment (500°C x 10 hours) and structure stabilization heat treatment (550°C x 15 hours). The product composition of the roll thus produced is shown in Table 2. Further, as a result of ultrasonic flaw detection performed on the body of the roll, it was confirmed that the outer shell and inner shell were completely connected. Furthermore, the results of microstructural observation of the outer shell of Example 1 are shown in FIG. As is clear from FIG. 2, it was confirmed that the desired structure consisting of fine graphite, chromium carbide, and matrix was obtained. Table 3 shows the results of examining the outer shell hardness and inner shell strength.

[Table] Next, the seizure resistance of the outer shell material was investigated by a fabrication test. (i) As shown in Figure 3, the fabilly test
One end of the test pin 11 is fixed to the rotating machine 12 with a shear pin 13, and the test pin 11 is rotated while the other end is held between a pair of V blocks 14 and 14 under a constant load P. The presence or absence of seizure depending on the torque,
This is to check the degree. (ii) The test conditions for the fabilly test were as follows. Test pin dimensions...φ6.5×40l V block dimensions...φ12 Test pin rotation speed...300rpm (0.1m/sec) Applied load P...35Kg Test environment...no lubrication (iii) Results of the fabilly test It is shown in FIGS. 4 and 5. FIG. 4 corresponds to the second embodiment, and FIG. 5 corresponds to the conventional example. A comparative material with the following components without crystallization of graphite was also tested, and the results are shown in FIG. Comparative material chemical composition (wt%) C: 2.86% Si: 0.92% Mn: 0.60% P: 0.072% S: 0.013% Ni: 7.40% Cr: 8.29% Mo: 0.73% Balance substantial Fe (iv) Figure 4 It can be seen that with the outer shell material according to the present invention, almost no increase in torque was observed and no seizure phenomenon occurred. On the other hand, with respect to the conventional shell material, which is a conventional high-chromium material, it can be seen from FIG. 5 that seizure began to occur after 12 seconds, and the seizure continued to occur strongly thereafter. Also, regarding the comparative material, which has almost the same components as the outer shell material of Example 1 except for Si, the sixth
Torque increases rapidly after 9 to 10 seconds as shown in the figure19
It reaches its maximum within seconds, indicating that burn-in has occurred. The thermal conductivity at 600°C was investigated for the shell material of Example 2, the conventional example, and the comparative material. The results are shown below. Thermal conductivity Cal/cm.seo.℃ Example 2 5.3×10 ^-2 Conventional example 5.4×10 ^-2 Comparative material 4.7×10 ^-2 From the above results, the thermal conductivity of the outer shell material of the present invention is equal to that of the conventional material. Although there was almost no change, a significant improvement was observed compared to the comparative material, which had almost the same composition. The reason why the thermal conductivity was almost the same as that of conventional materials is thought to be because the difference in components was greater than the presence or absence of graphite. However, from the hardness measurement results and seizure resistance test results, the outer shell of the present invention has superior wear resistance and especially seizure resistance compared to conventional high chromium materials, and furthermore, the overall As a result, it is clear that it has excellent roughening resistance, and it has also become clear that it has excellent crack resistance because the growth of cracks can be effectively inhibited by the formation of graphite. As explained above, the outer shell of the present invention has fine graphite crystallized in a chromium material with a high Ni content as it is cast, so it has excellent wear resistance, crack resistance, and especially seizure resistance. This resulted in excellent results, which in turn made a significant contribution to improving the roughness resistance. In addition, since the inner shell of the present invention has a relatively low Cr content in the outer shell, it is possible to reduce the mixing and diffusion of Cr from the outer shell to the inner shell, and improve the toughness of the inner shell. did it.

[Brief explanation of the drawing]

FIG. 1 is a sectional view schematically showing a structural example of a composite high chromium roll according to the present invention. Fig. 2 is a micrograph (50x magnification) showing the outer shell structure of an example roll of the present invention, Fig. 3 is an explanatory diagram of the fuabilly test procedure, and Figs. 4 and 5 are graphs showing the fuabilly test results. FIG. 4 shows an example shell material, FIG. 5 shows a conventional shell material, and FIG. 6 shows a comparative material. 1... Outer shell, 2... Inner shell (shaft core material).

Claims (1)

[Claims] 1 C2.4~3.4, Si2.0~3.4, Mn0.5~1.5, P0.1 or less, S0.08 or less, Ni4.5~10, Cr5~10, Mo0.4~
1.5% by weight, the remainder substantially consists of Fe,
A high chromium roll containing graphite, characterized in that an outer shell in which graphite is crystallized in its structure and an inner shell made of high-grade cast iron, ductile cast iron, or graphite cast iron are welded and integrated.